fix: use correct locktime and version in Taproot sighash

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## 1.0.0
 
+* Bugfix: Taproot sighash now uses actual transaction values instead of hardcoded locktime=0 and version=2 (#14)
 * Migrate code from `base` to `core`
 * *Breaking:* Remove `toBytes` function in `bitcoin/TxOutput.mo` (use class method instead)
 * *Breaking:* Add length assertions inside `Bech32.encode()`

src/bitcoin/Transaction.mo

@@ -265,10 +265,12 @@ module {
 
       let sighash_type : [Nat8] = [0x00];
       let nVersion_buffer = VarArray.repeat<Nat8>(0, 4);
-      Common.writeLE32(nVersion_buffer, 0, 2);
+      Common.writeLE32(nVersion_buffer, 0, version);
       let nVersion = nVersion_buffer.toArray();
 
-      let nLockTime : [Nat8] = VarArray.repeat<Nat8>(0, 4).toArray();
+      let nLockTime_buffer = VarArray.repeat<Nat8>(0, 4);
+      Common.writeLE32(nLockTime_buffer, 0, locktime);
+      let nLockTime = nLockTime_buffer.toArray();
       let sha_prevouts : [Nat8] = Sha256.fromArray(#sha256, prevouts.flatten()).toArray();
 
       let amounts_bytes = amounts.map<Nat64, [Nat8]>(

test/bitcoin/p2trKeyPathSigHash.test.mo

@@ -1,8 +1,11 @@
 import Blob "mo:core/Blob";
 import Nat "mo:core/Nat";
+import VarArray "mo:core/VarArray";
 
 import { expect; test } "mo:test";
 
+import Transaction "../../src/bitcoin/Transaction";
+import Witness "../../src/bitcoin/Witness";
 import TestVectors "p2trTestVectors";
 
 for (testCase in TestVectors.testCases().vals()) {
@@ -20,3 +23,51 @@ for (testCase in TestVectors.testCases().vals()) {
     },
   );
 };
+
+test(
+  "non-zero locktime changes sighash",
+  func() {
+    let testCase = TestVectors.testCases()[0];
+    let txLocktime0 = testCase.transaction();
+    let txLocktime42 = Transaction.Transaction(
+      TestVectors.version,
+      testCase.inputs(),
+      testCase.outputs(),
+      VarArray.repeat(Witness.EMPTY_WITNESS, testCase.numInputs),
+      42,
+    );
+
+    let hash0 = txLocktime0.createTaprootKeySpendSignatureHash(
+      testCase.amounts(), testCase.ownScript(), 0,
+    );
+    let hash42 = txLocktime42.createTaprootKeySpendSignatureHash(
+      testCase.amounts(), testCase.ownScript(), 0,
+    );
+
+    expect.blob(Blob.fromArray(hash0)).notEqual(Blob.fromArray(hash42));
+  },
+);
+
+test(
+  "different version changes sighash",
+  func() {
+    let testCase = TestVectors.testCases()[0];
+    let txVersion2 = testCase.transaction();
+    let txVersion1 = Transaction.Transaction(
+      1,
+      testCase.inputs(),
+      testCase.outputs(),
+      VarArray.repeat(Witness.EMPTY_WITNESS, testCase.numInputs),
+      0,
+    );
+
+    let hash2 = txVersion2.createTaprootKeySpendSignatureHash(
+      testCase.amounts(), testCase.ownScript(), 0,
+    );
+    let hash1 = txVersion1.createTaprootKeySpendSignatureHash(
+      testCase.amounts(), testCase.ownScript(), 0,
+    );
+
+    expect.blob(Blob.fromArray(hash2)).notEqual(Blob.fromArray(hash1));
+  },
+);

test/bitcoin/p2trScriptPathSigHash.test.mo

@@ -1,8 +1,12 @@
 import Blob "mo:core/Blob";
 import Nat "mo:core/Nat";
+import VarArray "mo:core/VarArray";
 
 import { expect; test } "mo:test";
 
+import P2tr "../../src/bitcoin/P2tr";
+import Transaction "../../src/bitcoin/Transaction";
+import Witness "../../src/bitcoin/Witness";
 import TestVectors "p2trTestVectors";
 
 for (testCase in TestVectors.testCases().vals()) {
@@ -20,3 +24,28 @@ for (testCase in TestVectors.testCases().vals()) {
     },
   );
 };
+
+test(
+  "non-zero locktime changes script spend sighash",
+  func() {
+    let testCase = TestVectors.testCases()[0];
+    let txLocktime0 = testCase.transaction();
+    let txLocktime42 = Transaction.Transaction(
+      TestVectors.version,
+      testCase.inputs(),
+      testCase.outputs(),
+      VarArray.repeat(Witness.EMPTY_WITNESS, testCase.numInputs),
+      42,
+    );
+
+    let leafHash = P2tr.leafHash(testCase.leafScript());
+    let hash0 = txLocktime0.createTaprootScriptSpendSignatureHash(
+      testCase.amounts(), testCase.ownScript(), 0, leafHash,
+    );
+    let hash42 = txLocktime42.createTaprootScriptSpendSignatureHash(
+      testCase.amounts(), testCase.ownScript(), 0, leafHash,
+    );
+
+    expect.blob(Blob.fromArray(hash0)).notEqual(Blob.fromArray(hash42));
+  },
+);